2003-09-01 04:00:00 PDT Mono Lake -- Brine shrimp dart in the shallows along this weirdly tower-studded lakeshore, and clouds of alkali flies darken patches of the lake's salty surface. But Richard Hoover, a onetime solar physicist, collects only a few of those mundane creatures.

He is on the hunt for stranger prey.

Glass tubes cram his pockets as he gathers samples of muck from the lake's rough and rubbled bottom. Some of the samples, he hopes, will reveal the presence of "extremophiles," microbes that inhabit some of the most bizarre environments on Earth.

An infinite variety of life forms has been found in environments that more familiar organisms can't tolerate. Hoover hopes that some of these places just might resemble the extreme environments where life may once have thrived on other worlds in our solar system.

The space probes that examine red-hued Mars, or giant Jupiter's icy moons Europa and Callisto, or ringed Saturn's smog-shrouded satellite Titan, are spurred by the possibility that life may well be far more widespread in the solar system -- or at least may once have existed in extreme environments other than on Earth alone.

But what might life be like in such alien places? Some of their environments are much too hot or cold to support the normal life of Earth's surface and its waters. Some are much too acid or alkaline, and the atmosphere on some may be much too dense or sparse for normal Earthly organisms.

Yet on Earth, such extreme environmental niches exist, and life inhabits them: in the boiling hot springs and geysers of Yellowstone; in ice layers thousands of feet beneath the surface of Antarctica; in the deepest metal mines of Asia; and in the muck of Mono Lake, where not a single fish can withstand the water's heavy burden of salt and alkalinity.

TRACKING EXTRATERRESTRIAL LIFE

His fixation on extraterrestrial life generates more than mild skepticism from other scientists who strongly question his insistence that some of the most notable meteorites that have ever struck Earth contain fossil life forms from other planets. Many of those meteorites bear curious markings that resemble fossils under the microscope and have evoked much controversy, but Hoover sticks to his guns.

"Hoover makes outlandish claims without any evidence," says Jeffrey Bada of UC San Diego's Scripps Institution of Oceanography, a geochemist and major researcher in the field. "He does not even appreciate what kinds of structures are associated with life, even here on Earth."

"That's ridiculous," says Hoover, an astrobiology group leader at NASA's Huntsville life science laboratory. "I can tell life when I see it, and I can tell fossil life forms, too -- wherever they exist."

On Hoover's side are a few microbe-hunting geologists, such as F. Leo Lynch,

a Mississippi State University geologist who argues that some meteorites bear the fossils of "nanobacteria" -- microorganisms that shrank in size from full- size microbes as they were hurled into space from other planets.

PASSION FOR WIFE, MICROBES

Hoover began his career at Huntsville as a solar X-ray physics researcher and was designing optics for solar telescopes when he met his wife-to-be in the Alabama city.

By chance, the young woman who was to become Mrs. Hoover possessed her great-grandfather's 19th century collection of microscope slides displaying a dizzying assortment of bacteria, algae and diatoms.

"I caught him with that collection," Miriam Hoover recalls over dinner at nearby Convict Lake. "He took one look at those beautiful little microbes under a microscope, and he was hooked."

Hoover accepted the lure. From bachelorhood and solar physics, he quickly moved to marriage and microbiology, and when space agency scientists intensified their exploration of Earth's microbial world to see what kinds of life forms might conceivably find their analogues on other planetary bodies, Hoover began hunting his "extremophiles."

Scrambling among the rocks of the Sierra's huge eastern scarp just above Convict Lake, Hoover found hot steam and water bubbling from the ground amid small, heavily alkaline lakes crowded with "absolutely gorgeous" white sulphur- eating bacteria that were thriving without oxygen. The region lies within what's known as the Long Valley Caldera, the weathered remains of a monstrous volcano that erupted 700,000 years ago. The caldera region still rumbles occasionally; moderate earthquakes shake the ground, and carbon dioxide gas still belches from fissures.

HAULING 'BEAUTIFUL CREATURES'

At Pyramid Lake, northwest of Reno, Hoover found "deep red and orange bacterial mats" in areas of the lake bottom where no oxygen exists, and he hauled up quantities of diatoms and unusual algae with their varied silica exoskeletons.

But it was at Mono Lake -- named for a branch of the Paiute Indian people whose word "mono" refers to the brine flies (Ephydra hians) whose pupal stages the Mono people consumed as salty food -- that Hoover found his richest haul.

"What beautiful creatures they are," he exclaims as he describes with more than a hint of rapture the three new species of bacteria he had already found during an earlier visit to the lake.

"It may take months in the lab before we can be sure of what I'm collecting today, but you never know, and in this kind of wonderful mud, with absolutely no oxygen and so heavily alkaline, we're bound to find more new ones -- the very kinds of microbes that could well be living -- or at least might once have lived -- somewhere else in the solar system."

Hoover and his research colleague at Huntsville, microbiologist Elena Pikuta, have already identified three new species of bacteria they have found in Hoover's avid quest at Mono Lake. They bear formidable names: Spirochaeta americana, Tindallia californiensis, and Desulfonatronum thiodismutans.

The last one, D. thiodismutans, is particularly notable, Hoover says, because it apparently lives and obtains its energy by metabolizing sulfur -- the very element that sustains bacterial life at the base of the food chain in deep-sea hydrothermal vents, miles beneath the sea where there is neither light nor oxygen and where fiery volcanic heat dominates the environment.

Hoover has sought his microbial trophies in some of the most remote places on Earth, including the Russian Antarctic research station called Vostok, where temperatures often reach 130 degrees below zero.

That outpost sits atop more than 2 miles of ice, and far below it lies a mysterious lake almost 125 miles long and 3,200 feet deep -- twice the depth of Tahoe -- which American and Russian scientists would dearly love to explore.

The Russians discovered it in 1996, but no one knows how such a lake of water can exist unfrozen beneath all those miles of ice, nor how much old and empty air exists between the lake's surface and the ice above it.

But if living organisms exist in the lake's waters, they must have been reproducing in that environment for 300 million years or more -- since the time when the wandering Antarctic continent lay athwart the equator and tropical vegetation grew there.

FINDING COMMON GROUND IN ICE

The Russians, with American help, drilled a hole through the Vostok ice toward the lake and stopped when their drill reached a depth of 11,900 feet for fear of breaking through the ice and contaminating the pristine lake.

For several years now, teams of Russian and American scientists have sought to devise a way of probing the lake itself with some kind of meticulously sterile robot minisubmarine, but no one has yet figured out just how to do it.

Hoover and his Russian colleague, Sabit Abyzov, have been examining ice core samples from the Vostok drilling project that are as much as 400,000 years old. And living in the ancient ice are fungi, algae, bacteria, protozoa and diatoms.

"That ice must be very much like the icy crust of Jupiter's moon Europa," Hoover says, "so is it too much to wonder whether all kinds of similar forms of life have existed up there, too?"

Hoover notes that the geologic basin in which Mono Lake lies resembles a prominent feature on Mars called Gusev Crater, where NASA's Mars robot rover named Spirit will land early next year. Gusev Crater surely holds no water today, but it may contain fossil evidence of past life. Hoover hopes the extremophiles he picks up in Mono's alkaline waters may help scientists understand the ancient life of such fossils -- if ever they are found on Mars.